The present invention relates to a method of improving the quality of dam obtained by logging a borehole and, more particularly, to a method of enhancing the vertical resolution of well logging data.
Dual-spaced neutron and density logging tools, using ratio processing and spine and rib plots, respectively, provide borehole compensated formation porosity measurements. The effects of washout, mudcake, rugose boreholes, and tool standoff are thereby minimized. Standard shop calibration procedures insure porosity measurement accuracy.
The preprocessing (or preliminary) operations of depth alignment and material matching are critical for accurate borehole compensation with dual detector logging tools; these operations also eliminate horns or spurious beds on logs. These preliminary operations involve material matching to improve accuracy and repeatability, but at the cost of degraded vertical resolution. Because of present limitations on the far neutron source-to-detector spacing, it is not possible to achieve a vertical resolution of better than about two feet while maintaining material matching using simple filtering methods.
During the past several years, new data processing methods have been developed to improve the vertical resolution of both neutron and density logging tools. For example, the near detector log profile from each tool is used (separately) to alter the vertical profile of the original borehole compensated log to thereby improve vertical resolution. These processing methods require modifications to standard shop calibrations of both tools. Although bed resolution appears to improve, statistical precision and/or log repeatability is degraded and porosity accuracy in rugose boreholes is compromised.